Such light integrating spherical devices have heretofore been used with spectrophotometers and the like, embodying a diffusely reflecting coating, film or layer adhered to the inside of a hollow-spherical surface provided with an appropriate aperture for injecting a light beam for reflection from a holder-held sample exposed at an opposing aperture, or at the center, and/or for transmission through a sample for diffuse reflection transmittance measurements by an appropriate detector monitoring the reflections from the spherical surface, as is well known.
Among the previously used diffuse reflecting coatings, films or layers have been packed or sprayed coatings of barium sulfate, magnesium oxide and/or magnesium carbonate, with a more recently suggested fluorinated aliphatic long chain addition polymer film, alone or coated on a substrate, applied to the inner surface of a hollow sphere, as described in U.S. Pat. Nos. 3,764,364 and 4,035,085. The difficulties with coatings as of barium sulfate and the like reside in sensitivity to moisture and other environmental conditions, degradation with ultraviolet light, relatively low reflectance and efficiency in the ultraviolet and infrared spectra, and mechanical instability in use including under conditions of rough handling, with coating dislodging, and non-susceptibility to cleaning. The problems with the suggested polymer film reside in such mechanical instability and lack of cleanability, also, though, as also recognized in U.S. Pat. No. 4,912,720 of common assignee herewith, improved reflectivity in the ultraviolet and infrared regions can be thereby obtained. The general difficulty of adherence and the different coefficients of expansion and contraction and other environmental responses of coatings or films and the surfaces against which or to which they are applied is also inherent in such prior art integrating spheres.